Fix generation of bundled.json, make source maps work in prod builds

Summary:
This diff fixes several issues around loading plugin, such as:

* make suresource maps work in the flipper-server production build
* make sure default plugins are no symlinked, which wouldn't work anywhere else but on the the system where it was build
* support release channel param for flipper-server

Bundled flipper-server is now 42MB (with icons (see later diffs) and plugins
```
ll flipper-server-v0.0.0.tgz
-rw-r--r--  1 mweststrate  staff    42M 23 Dec 15:29 flipper-server-v0.0.0.tgz
```

Reviewed By: nikoant

Differential Revision: D33294677

fbshipit-source-id: 63538dc8127f883fee6a3608673ad11ce239b350

desktop/scripts/build-utils.ts

@@ -420,9 +420,6 @@ export async function compileServerMain(dev: boolean) {
     resetCache: !dev,
   });
   console.log('✅  Compiled server bundle.');
-  if (!dev) {
-    stripSourceMapComment(out);
-  }
 }
 
 // TODO: needed?
@@ -503,9 +500,6 @@ export async function buildBrowserBundle(dev: boolean) {
     inlineSourceMap: false,
   });
   console.log('✅  Compiled browser bundle.');
-  if (!dev) {
-    stripSourceMapComment(out);
-  }
 }
 
 async function dedupeFolders(paths: string[]): Promise<string[]> {